Angiogenesis is the process whereby new blood vessels are formed. Angiogenesis, also called neovascularization, occurs normally during embryogenesis and development, and occurs in fully developed organisms during wound healing and placental development. In addition, angiogenesis occurs in various pathological conditions, including in ocular diseases such as diabetic retinopathy and macular degeneration due to neovascularization; in conditions associated with tissue inflammation, such as rheumatoid arthritis and inflammatory bowel disease; and in cancer, where blood vessel formation in the growing tumor provides oxygen and nutrients to the tumor cells, as well as providing a route via which tumor cells metastasize throughout the body.
In order to grow, a tumor must undergo an angiogenic switch. Vascular endothelial growth factor (VEGF) is required to induce this angiogenic switch. VEGF and the genes in the VEGF pathway are considered important mediators of cancer progression. Micro-vascularization in the tumor microenvironment may be reflective of the generation of new micro vessels induced by cancerous tissue to draw nutrients to support tumor growth. In addition, micro vessel density is indicative of tumor growth.
The importance of this pathway in cancer cell growth and metastasis has led to the development of anti-angiogenesis agents for use in cancer therapy. These therapies include, among others, bevacizumab, pegaptanib, sunitinib, sorafenib and vatalanib. Identification of patients that may respond to therapy with such agents is an important step in treating patients inflicted with cancer.